The long-term objective of this research is to quantify the contributions of three-dimensional semicircular canal thermo-mechanics as it related to health and the human condition. Present work includes three specific aims: l) biomechanics of canalolithiasis and its relationship to benign positional vertigo (BPV), 2) biomechanical and biophysical substrates of caloric nystagmus and, 3) spatio-temporal distribution of cupula/hair-bundle micro mechanics. The first aim will detail biomechanical and neural responses under conditions of experimentally induced canalolithiasis during provocative diagnostic tests and during canalith repositioning procedures. The second aim will separate traditional origins of caloric nystagmus -- temperature-dependent fluid buoyancy and hair-cell/afferent excitability -- from the influence of local thermal expansion and Tran labyrinthine pressure. Results will address the origin of asymmetric caloric nystagmus and caloric responses under hypo- and hyper-gravity. Both of these aims have direct clinical relevance in understanding, diagnosing and treating specific vestibular disorders. The third aim addresses micro mechanical contributions in shaping the neural code transmitted to the brain stem. Several lines of investigation indicate that sensory hair cells located within various regions of the sensory epithelium receive differing mechanical inputs. We will directly measure regional differences in cupula and hair bundle motion. Experiments to investigate the possible role of hair cell/bundle motility will be included. The influence of activation of the efferent vestibular system and, separately, electrical polarization of the endolymph on hair bundle displacements will be determined. Detailed mathematical models will be used extensively to interpret results and direct the experimental studies. The experimental model will be the oyster toadfish, Opsanus tau. The fundamental structure of the semicircular canals is ancient and shows remarkable similarity across vertebrates ranging from fish to man. This enables the use of a relatively primitive species for these studies to address important issues relevant to sensory physiology and health in human.